1. Field of the Invention
The present invention relates to a radiation thermometer and particularly to an improvement of calibration means and the like in a radiation thermometer for measuring temperature of a target object based on radiation energy emitted from the target object.
2. Description of the Prior Art
Various radiation thermometers for calculating the temperature of a target object based on radiation energy are known in the prior art. In order to reduce the manufacturing cost in such a radiation thermometer, it is necessary to consider a reduction in cost required for calibration as well as, or much more than a reduction in the costs of parts or an assembling cost. More specifically, in the case of such radiation thermometers, characteristics of components such as a detector for receiving radiation from a target object vary or show some irregular difference for each of the thermometers concerned and therefore calibration is indispensable for each thermometer.
Thus, in the prior art, various components such as a variable resistor for calibration are adjusted at the time of manufacturing a radiation thermometer. However, such adjustment work is extremely complicated.
Particularly, in a radiation thermometer using a pyroelectric device as a detector of radiation energy, a chopper is provided in front of the detector so that input of radiation energy to the detector can be intermittently changed, because an output signal corresponding to the radiation energy can not be obtained from the pyroelectric device unless an input signal to the detector is converted to an AC signal form. In such a structure, it is necessary to rectify an output signal of the detector in synchronism with the opening and closing of the chopper so that a detected output can be obtained in good condition. More specifically, although it is known that a phase of an output of a pyroelectric detector is delayed by approximately 90.degree. with respect to input energy, such phase delay varies for each radiation thermometer since characteristics of components, such as the detector per se, an amplifying circuit for amplifying the output thereof or a chopper driving circuit, differ for each thermometer. Consequently, calibration work is required for each radiation thermometer to compensate for the phase delay. For this purpose, calibrating components are adjusted conventionally by observing an output signal of a rectifying circuit using an oscilloscope or the like at the time of manufacturing a radiation thermometer so as to generate a synchronous rectifying signal for operating the rectifying circuit without such phase delay as described above. However, such adjustment work is extremely troublesome and requires much skill.
In addition, such calibration work is also indispensable not only for compensation for phase delay as described above but also for calibration for eliminating error factors due to the difference for each optical system or each detector at the time of calculating temperature of a target object or for calibration for eliminating error factors due to a difference for each sensor of reference temperature at the time of detecting the reference temperature around the detector. Accordingly, in addition to adjustment of a plurality of variable resistors used as calibrating components, it is necessary in the prior art to effect complicated calibration work such as setting of calibration data to a DIP switch or fitting of a PROM containing calibration data into the main body of the thermometer during or after assembling of a radiation thermometer.
Furthermore, recalibration of a radiation thermometer is sometimes required as after-sales service and in such cases, it is necessary to effect again calibration work such as the above described adjustment of variable resistors, operation of a DIP switch by removing a cover, or replacement of PROM's, which is extremely troublesome.
In the conventional radiation thermometers, a large number of keys such as an emissivity setting key and various mode setting keys are provided on an operation panel, which makes the operation to be complicated. Therefore, improvement in operation efficiency is desired. Particularly as for the emissivity setting switch, by which emissivity can be changed also during measurement of temperature for convenience, it sometimes happens to the contrary that this switch is erroneously operated in vain, causing the set emissivity to be changed and making it difficult to obtain an accurate calculated value of temperature.